1. Field of the Invention
The present invention relates to a belt transmission mechanism having a belt trained under tension around a crowned drive pulley and a crowned driven pulley.
2. Description of the Related Art
There has heretofore been known a belt transmission mechanism which comprises a drive pulley coupled to a motor, a driven pulley having a diameter that is the same as or different from the diameter of the drive pulley, and a flat belt trained around the drive and driven pulleys. When the motor is energized, the driven pulley is rotated by the drive pulley and the belt at a predetermined transmission ratio.
The transmission ratio between the drive and driven pulleys is determined by the diameters of the drive and driven pulleys and the speed at which the belt travels. The rotational speed of the motor is transmitted to the driven pulley while being reduced or increased to a certain rotational speed by the transmission ratio.
Many drive and driven pulleys are crowned, i.e., have convex circumferential surfaces of arcuate cross section in the axial direction, for preventing the belt from being laterally dislodged from the drive and driven pulleys. If the tension of the belt varies, then the belt is elongated to different degrees on the drive and driven pulleys due to the combination of the radii of the convex surfaces of the crowned drive and driven pulleys, resulting in a change in the transmission ratio.